1. Field of the Invention
This invention relates to solar collectors, and more particularly to a solar collection and distribution system including a collector that tracks the sun in elevation and azimuth, and a distribution system that directs a beam of sunlight along a ceiling or rooftop.
2. Background Information
There are various arrangements for solar radiation collection, distribution and utilization. Most suffer numerous surface reflection loses are of impractical design, have insufficient visible light collection capability, and lack adaptability to diverse end-uses.
It might seem obvious to use a sun-tracking mirrored dish system to collect and transmit sunlight. Such a system could use a prime focus parabolic reflector, and a secondary reflector to focus the sunlight collected in a condensed, collimated beam back along the same axis through the primary reflector. The focused light could then reflect off a downward-directing planar reflector that would direct the light into a buildings or to an energy receiver. There must also be a means of effectively distributing the collected light and/or infrared radiation. There are, however, inherent problems and inefficiencies with such a prime focus three-reflector design, particularly at high sun elevations.
The first problem with a prime focus collector of such design is that to transmit most of a collimated beam at high sun elevations (using a practical beam diameter and concentration levels), the planar reflector must be of impractical length. With practical lengths, typically half of a beam""s cross-section cannot be redirected by the planar reflector when the sun is nearly overhead. Using too small a beam diameter to increase the percentage of light captured and reflected at high sun elevations generally results in a concentration level so high that system materials are likely to degrade and also increases the risk of fire and other safety hazards.
Secondly, since the angle of incidence at the downward-directing planar reflector increases with increasing sun elevation, there are substantial surface reflection losses at high sun elevations when a standard reflecting material such as glass mirror is used for the planar reflector, in addition to undesirable spectral absorption characteristics and color shifting, even when a state of the art first surface specular reflecting material such as enhanced reflectivity anodized sheeting is used.
Thirdly, at high sun elevations, the cross-sections of a planar reflector and its supporting structure begin to occlude the collimated beam from the secondary reflector, significantly reducing system output and efficiency.
It is therefore a principal object and advantage of the present invention to minimize transmission losses in a solar radiation collection system at sun elevation angles above about 75xc2x0. It is a further object and advantage of the invention to provide a solar radiation collection and distribution system which maximally and efficiently collects, collimates, spectrally separates and distributes solar radiation at all latitudes and sun elevation angles, and is adaptable to multiple uses including illumination, heating, cooling, water purification, photobioreactors and electric power generation.
The invention provides a solar radiation collection and distribution system including a solar collection system which includes a primary reflector having an aperture, and a secondary reflector which redirects solar radiation received from the primary reflector in a concentrated beam through the aperture. The primary and secondary reflectors are rigidly disposed in a pivotable assembly. The beam has an exit angle with respect to the assembly which is different than the angle at which solar radiation is incident on the primary reflector. The solar collection system further includes means for pivoting the assembly in elevation at an angular rate such that the primary reflector continuously tracks the sun, and means for annularly rotating the assembly such that the primary reflector continuously tracks the sun in azimuth. The solar collection system further includes a pivotable planar reflector which receives and reflects downwardly the beam from the secondary reflector, and pivots at one-half the angular rate at which the assembly pivots. The downwardly reflected beam consists essentially of sunlight and is maintained in a substantially constant vertical and horizontal orientation independent of the elevational and azimuthal motion of the assembly. The invention further provides a distribution system which includes a lateral reflector which reflects the beam reflected from the planar reflector, and a plurality of reflectors which each reflect downwardly a portion of the beam reflected from the lateral reflector.